A Denver inventor has created something called the Tapit Cap that will twist on to just about any growler, and uses a carbon dioxide system to create a miniature draft line on those bottles.

Here’s the thing about beer growlers. Those take-home bottles of beer are a great bargain, but they have a shelf life.

As long as they are never opened and kept cold, they can last days or weeks or sometimes longer. But the minute after you twist off the lid and pour a pint, the clock starts ticking. Air is the mortal enemy of beer. So while it’s better to finish off a growler immediately after it is opened, that raises problems for solo drinkers who just don’t want to drink that much beer at one time.

This may have finally been solved by Denver inventor Robert Scott, who has created something called the Tapit Cap. This simple system will twist on to just about any growler, and uses a carbon dioxide system to create a miniature draft line on those bottles. Small chargers dispense gas into the bottles and will keep beer carbonated and brewery fresh, no matter how little liquid remains. Mike Rangel, president of Asheville Brewing, purchased some of these Tapit Caps and said they work as promised.

The Tapit Cap will fit on any standard 64- or 128-ounce glass growler, Scott said. Because some beer drinkers favor growlers with flip-top lids or steel growlers, he is working on adapters. But for now, use the Tapit Cap on glass bottles with screw-off lids.

Scott funded the invention through a successful online Kickstarter campaign. He is selling the Tapit Caps online for $45. A six-pack of gas cartridges is $9.85. So far, he’s sold 4,000 Tapit Caps. You can order them at tapitcap.com.